In the proposed studies, the investigators plan to utilized the structural information to prepare a library of specific mutations designed to systematically alter the TR LBD surface such that interactions with other proteins involved in various TR functions might be disrupted. It is also planned to prepare mutations that should influence the function of two regions termed tau-3 and tau-4 thought to be involved in TR LBD transcriptional activation functions and of a Helix region (Helix-1) that maybe involved in various TR functions. Activities of mutated molecules will be examined through assays of T3 binding (TR + T3) binding to DNA and other proteins and by transfecting genes that express the mutated TRs along with reporter genes and genes that express other proteins that interact with TRs in mammalian cells.